The Complete Aristotle (eng.)

between them).
This is universally true wherever one thing is moved by another.
And since there are three kinds of motion, local, qualitative, and
quantitative, there must also be three kinds of movent, that which
causes locomotion, that which causes alteration, and that which
causes increase or decrease.
    Let us begin with locomotion, for this is the primary motion.
Everything that is in locomotion is moved either by itself or by
something else. In the case of things that are moved by themselves
it is evident that the moved and the movent are together: for they
contain within themselves their first movent, so that there is
nothing in between. The motion of things that are moved by
something else must proceed in one of four ways: for there are four
kinds of locomotion caused by something other than that which is in
motion, viz. pulling, pushing, carrying, and twirling. All forms of
locomotion are reducible to these. Thus pushing on is a form of
pushing in which that which is causing motion away from itself
follows up that which it pushes and continues to push it: pushing
off occurs when the movent does not follow up the thing that it has
moved: throwing when the movent causes a motion away from itself
more violent than the natural locomotion of the thing moved, which
continues its course so long as it is controlled by the motion
imparted to it. Again, pushing apart and pushing together are forms
respectively of pushing off and pulling: pushing apart is pushing
off, which may be a motion either away from the pusher or away from
something else, while pushing together is pulling, which may be a
motion towards something else as well as the puller. We may
similarly classify all the varieties of these last two, e.g.
packing and combing: the former is a form of pushing together, the
latter a form of pushing apart. The same is true of the other
processes of combination and separation (they will all be found to
be forms of pushing apart or of pushing together), except such as
are involved in the processes of becoming and perishing. (At same
time it is evident that there is no other kind of motion but
combination and separation: for they may all be apportioned to one
or other of those already mentioned.) Again, inhaling is a form of
pulling, exhaling a form of pushing: and the same is true of
spitting and of all other motions that proceed through the body,
whether secretive or assimilative, the assimilative being forms of
pulling, the secretive of pushing off. All other kinds of
locomotion must be similarly reduced, for they all fall under one
or other of our four heads. And again, of these four, carrying and
twirling are to pulling and pushing. For carrying always follows
one of the other three methods, for that which is carried is in
motion accidentally, because it is in or upon something that is in
motion, and that which carries it is in doing so being either
pulled or pushed or twirled; thus carrying belongs to all the other
three kinds of motion in common. And twirling is a compound of
pulling and pushing, for that which is twirling a thing must be
pulling one part of the thing and pushing another part, since it
impels one part away from itself and another part towards itself.
If, therefore, it can be shown that that which is pushing and that
which is pushing and pulling are adjacent respectively to that
which is being pushed and that which is being pulled, it will be
evident that in all locomotion there is nothing intermediate
between moved and movent. But the former fact is clear even from
the definitions of pushing and pulling, for pushing is motion to
something else from oneself or from something else, and pulling is
motion from something else to oneself or to something else, when
the motion of that which is pulling is quicker than the motion that
would separate from one another the two things that are continuous:
for it is this that causes one thing to be pulled on along with the
other. (It might indeed be thought that there is a form of pulling
that arises in another way: that wood, e.g. pulls fire in a manner
different from that described above. But it makes no difference
whether that which pulls is in motion or is stationary when it is
pulling: in the latter case it pulls to the place where it is,
while in the former it pulls to the place where it was.) Now it is
impossible to move anything either from oneself to something else
or something else to oneself without being in contact with it: it
is evident,